At present there are many applications for voice processing systems which are interconnected in a wide area telephone network. For example, in one instance of such an application, voice messages are transmitted among voice processing systems, sometimes referred to in the art as voice processing nodes, which are connected to the wide area network over voice grade telephone lines.
As is well known in the art, the process of transmitting a recorded message from a first, sending voice processing system over a voice grade telephone line for re-recording at a second, receiving voice processing system is sensitive to the transmission quality of the voice grade telephone line. For example, any noise, attenuation, or other such transmission impairment will degrade the quality of the re-recorded message and possibly make it difficult to understand. As a result of this, there is a need in the art to be able to measure the amount of certain types of transmission impairments to voice grade telephone lines so that systems which communicate over these lines, for example, voice processing systems, can take appropriate action if the measured transmission impairments exceed predetermined thresholds. One example of an appropriate action includes the sending voice processing system's electing to abort a communication and trying to complete the communication using a different voice grade telephone line.
There presently exist several methods for measuring transmission quality which are known in the art. One example of such a method is to use specific equipment such as transmission impairment measurement sets (TIMS) such as the model HP 4937A test set which is available from Hewlett Packard of Palo Alto, Calif. Another example of such a method is the use of high speed modems which use dial-up, voice grade telephone lines, to perform transmission quality measurements. In fact, such methods sometimes include special apparatus for use in compensating the transmitted signals for the degradations introduced therein by the measured impairments to the voice grade telephone line. Such methods have a serious drawback when they are used with interconnected voice processing systems. This drawback occurs because additional equipment is required and this additional equipment requires the voice processing systems to have added space and, thereby, added cost.
As one can readily appreciate from the above, there is a need in the art for apparatus and method for measuring the transmission quality of telephone channels in a telephone network. Further, there is an additional need for such apparatus and method which can be used in connection with interconnected voice processing systems without adding additional equipment to the voice processing systems and/or to the telephone network.